linux-kernel - Re: [PATCH v4 06/17] virt: acrn: Introduce VM management interfaces

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Date:   Mon, 28 Sep 2020 14:29:34 +0800
From:   Shuo A Liu <shuo.a.liu@...el.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     linux-kernel@...r.kernel.org, x86@...nel.org,
        "H . Peter Anvin" <hpa@...or.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Yu Wang <yu1.wang@...el.com>,
        Reinette Chatre <reinette.chatre@...el.com>,
        Zhi Wang <zhi.a.wang@...el.com>,
        Zhenyu Wang <zhenyuw@...ux.intel.com>
Subject: Re: [PATCH v4 06/17] virt: acrn: Introduce VM management interfaces

On Mon 28.Sep'20 at  7:25:16 +0200, Greg Kroah-Hartman wrote:
>On Mon, Sep 28, 2020 at 11:50:30AM +0800, Shuo A Liu wrote:
>> > > +	write_lock_bh(&acrn_vm_list_lock);
>> > > +	list_add(&vm->list, &acrn_vm_list);
>> > > +	write_unlock_bh(&acrn_vm_list_lock);
>> >
>> > Why are the _bh() variants being used here?
>> >
>> > You are only accessing this list from userspace context in this patch.
>> >
>> > Heck, you aren't even reading from the list, only writing to it...
>>
>> acrn_vm_list is read in a tasklet which dispatch I/O requests and is wrote
>> in VM creation ioctl. Use the rwlock mechanism to protect it.
>> The reading operation is introduced in the following patches of this
>> series. So i keep the lock type at the moment of introduction.
>
>Ok, but think about someone trying to review this code.  Does this lock
>actually make sense here?  No, it does not.  How am I supposed to know
>to look at future patches to determine that it changes location and
>usage to require this?

OK. May i know how to handle such kind of code submission? Or which way
following do you prefer?
  1) Use a mutex lock here, then change it to rwlock in a later patch
     of this series.
  2) Add more comments in changelog about the lock. (Now, there is
     comment around the acrn_vm_list_lock)

>
>That's just not fair, would you want to review something like this?
>
>And a HUGE meta-comment, again, why am I the only one reviewing this
>stuff?  Why do you have a ton of Intel people on the Cc: yet it is, once
>again, my job to do this?

The patchset has been reviewed in Intel's internal mailist several
rounds and got Reviewed-by: before send out. That's why i Cced many
Intel people as well.

This patchset is all about a common driver for the ACRN hypervisor
support. I put the code in drivers/virt/ and found you are one of the
maintainer of vboxguest driver which is in the same subdirectory. I
thought you should be the right person to be Cced when i submitted this
series.

Certainly, any comments are welcome. And really appreciate your review
and help. I have little experience to submit a new driver to the
community, my apologies if thing goes wrong.

Thanks
shuo